In recent years, in order to accomplish microsizing, high speed and energy saving for an image-forming apparatus employing electrophotography, the toner for developing an electrostatic charge image to be used for such an apparatus, is required to have low temperature fixing properties. In order to improve the low temperature fixing properties of a toner, it is important not only to lower the lower limit of the fixing temperature but also to broaden the fixing temperature range of the toner. Heretofore, in order to accomplish such objects, it has been attempted to use a component having a relatively low molecular weight and a component having a relatively high molecular weight in combination as the binder resin containing the toner. However, in such a method, the low molecular weight component has sometimes caused deterioration of the electrostatic property of the toner. Further, there has been a problem that when such a toner is used for a long period of time, the low molecular weight component tends to soil the carrier, photoreceptor, developing blade, etc., whereby no clear images have been obtained.
Further, it has been attempted to improve the low temperature fixing properties of a toner by incorporating wax to the toner. If wax is incorporated to the toner, it is possible to prevent the toner softened during the fixing from fusing to the fixing roller, whereby a wide fixing temperature range can be secured. Particularly, with a toner prepared by an emulsion polymerization flocculation method (e.g. JP-A-9-190012) or a toner obtained by a suspension polymerization method (e.g. JP-A-8-050368), the content of wax in the toner can be increased, as compared with the toner obtained by a melt kneading pulverization method. If a toner containing wax is produced by a wet system polymerization method such as an emulsion polymerization flocculation method or a suspension polymerization method, it is possible to obtain a toner which can realize relatively low temperature fixing. However, if wax is incorporated in a large amount in the toner, in many cases, the wax tends to leach out on the toner surface. And, the leached out wax tends to cause deterioration of the electrostatic property of the toner. Further, there has been a problem that if a toner containing a large amount of wax is used for a long period of time, wax leached out from the toner tends to soil components of the apparatus such as the carrier, photoreceptor and developing blade, whereby clear images can hardly be obtainable. Further, excessive wax hinders fixing of the toner on the fixing substrate such as paper, thus leading to deterioration of the fixing strength. From this viewpoint, among conventional waxes, there has been one having a release property with a view to preventing offset (fusion) to the fixing roller, but there has been none which has affinity to the fixing substrate such as paper and which has a reinforcing effect at the time of fixing the toner.
Further, in a case where a full-color image is to be formed by superimposing toners of various colors such as cyan, magenta, yellow and black, it becomes more important to secure a wide fixing temperature range and to improve the fixing strength to the fixing substrate.
Further, in recent years, as a developing system, a non-magnetic one component system has been used in many cases. In the case of this system, the mechanical stress is high when the toner is formed into a thin layer on a developing roller. Accordingly, in the case of the non-magnetic one component system, the above-mentioned various problems resulting from leaching of wax or a low molecular weight component in the binder resin from the toner, have been more distinct. Especially in a case where an organic photoconductor (hereinafter sometimes referred to simply as OPC) is used, and development is carried out by pressing a thin layer of the toner on the developing roller directly against OPC, i.e. in a case where so-called contact phenomenon is employed, wax or a low molecular weight component in the binder resin tends to cause filming on OPC, thus leading to a fatal trouble. As a method to prevent leaching of such a component from the toner, a method of increasing the molecular weight of a high molecular weight component in the binder resin is conceivable, but in such a case, the low temperature fixing properties tend to deteriorate. Consequently, it has been difficult to satisfy both the durability and the fixing properties of the toner. Thus, it has not been known heretofore how to obtain a toner which has a good low temperature fixing property, a wide fixing temperature range and high fixing strength and which is stable in the electrostatic property even when it is used for a long period of time and free from soiling of the apparatus.